Assad regime forces carried out an airstrike near a Turkish military convoy in northern Syria on Monday, in a rare example of Damascus directly confronting Turkish troops operating inside Syria.
At least one pro-Turkey fighter was killed in the strike and several were injured, according to the Syrian Observatory for Human Rights. It was not clear if the casualties were Turkish soldiers or Syrian rebels backed by Turkey.
The Syrian regime earlier condemned the military convoy, which it said was carrying weapons for Syrian rebels fighting against regime forces in the town of Khan Sheikhoun, in the south of the opposition-held province of Idlib.
Syrian state media said the convoy was “heading towards Khan Sheikhoun to help the terrorists…which confirms once again the support by the Turkish regime to terrorist groups”.
Turkey's defence ministry "strongly" condemned the attack, which it said had killed three civilians and wounded 12.
"Despite repeated warnings we made to the authorities of the Russian Federation, the military operations by the regime forces continue in Idlib region in violation of the existing memorandums and agreements with the Russian Federation," it said in a statement.
Videos on social media appeared to show the Turkish convoy had halted its advance and was waiting on the side of the motorway.
Turkish forces maintain a number of outposts in Idlib, which they say are used for combatting jihadist groups and maintaining a ceasefire brokered by Turkey and Russia.
The Assad regime frequently complains about the Turkish presence in Syria, saying it is a violation of Syrian sovereignty and is designed to help terrorist groups, but rarely takes direct action against the Turks.
Assad regime forces stepped up their offensive against rebel forces in Idlib in April and have made territorial advances with the support of Russian airpower. At least 500 civilians have been killed since the offensive began, according to the UN.
Rebel forces are led by Hayat Tahrir al-Sham, a jihadist group with links to al-Qaeda.
Syrian forces are now on the outskirts of Khan Sheikhoun and are fighting to drive rebel fighters out. The town is best known as the site of an Assad regime chemical weapons attack in April 2017, when nearly a hundred people were killed by poison gas.
Donald Trump ordered airstrikes against a Syrian regime airbase in response to the attack.